Lubricating compositions



Patented Dec. 26, 1950 2,535,024 LUBRIOATING COMPOSITIONS Charles Earle Funk, Jr., Cos Cob, Conn., assignm- -to American Cyanamid Company, New York, N. Y., a corporation of Maine e No Drawing. Application January 13, 1948.

Serial No. 2,132

3 Claims.

This invention relates to the production of improvement agents for lubricating oils, and relates more particularly to the production of mineral oil solutions of heavy metal salts of esters of dithiophosphoric acid which are suitable for use as antioxidant and detergent agents in the improvement of lubricating oils. The present application is a continuation-in-part of application Serial No. 643,749, filed January 26, 1948 (now abandoned).

Lubricating oil addition agents having particularly desirable detergent and antioxidant qualities are the heavy metal salts of esters of dithiophosphoric acid, which are formed by reacting alkyl or alkaryl compounds with phosphorus pentasulflde and neutralizing the acids so produced with oxides or hydroxides containing various heavy metals such as calcium, barium, zinc, tin, and the like.

Heretofore. it has been necessary to carry out the dithiophosphoric acid ester neutralization in the presence of polar and non-polar solvents such as solvent mixtures comprising small amounts of the lower alcohols together with greater amounts of indifferent volatile hydrocarbon solvents such as toluol, and the like. 'I'he non-polar solvents acted as diluents for the reactants, while the polar solvents furnished the ionizable medium necessary for the reaction between the esters of dithiophosphoric acid and the basic materials employed. In some instances, it has also been practicable to employ water instead of the above men- 2 these dithiophosphoric acid esters may advantageously be carried out in a mineral oil solution and/or dispersion in the presence 01' an amount of methanol small enough as to render its subsequent removal unnecessary.

Thus the primary object of this invention resides in the provision of a method of producing heavy metal salts of esters of dithiophosphoric acid in mineral oil solution and/or dispersion, whereby solvent recovering may be dispensed with, resulting in the elimination of a troublesome and expensive operational procedure.

A further object oi the invention is the prevention of decomposition of these improvement agents for lubricating oils by the elimination of the relatively high temperatures which have previously been necessary for effecting removal of solvent material therefrom.

In its broader aspects the method of my in- 2 vention consists in the addition of an ester of tioned solvents to provide a medium in which the reactants possessed mutual solubility. The use of these solvents was decidedly disadvantageous because it was necessary to strip the solvent materials subsequent to the salt-forming treatment. Solvent removal was necessary because the presence of such materials in the addition agents in amounts in excess of about 5% caused a lowering of the flash point of the oils to which they are added below the specifications which have been adopted by the industry. Ordinarily, the stripping of the solvents from the additives was carried out either at relatively elevated temperatures or under reduced pressure at somewhat lower temperatures. When the solvent removal was carried out at elevated temperatures there was great danger that the lubricating oil additive would undergo excessive deterioration. When the solvent removal was carried out by resorting to reduced pressure at relatively lower temperatures, the cost of the operation was almost prohibitive.

I have discovered that the neutralization of dithiophosphoric acid to'a dispersion in mineral oil of an oxide or hydroxide of a heavy metal in the presence of a small amount oi methanol. The dithiophosphoric acid esters suitable for use in the present invention include monoalkyl, dialkyl, monoalkaryl, and dialkaryl esters of dithiophosphoric acid which may be produced from primary alcohols such as 2-methyl pentanol-l, 2,4-dimethyl pentanol-l, ii-methyl hexanol-l, 4- methyl heptanol-l, and the like, and secondary alcohols such as di-isopropyl carbinol, and the like. Alkaryl compounds which are exceptionally suitable for producing these dithiophosphoric acid esters include monoand di-alkyl phenols, including tri-isobutyl phenol, di-octyl phenol, and the like compounds.

Neutralization of the above described acid materials may be carried out over a relatively wide temperature range, as for example from about 20 C. to about C. Although the neutralization may be carried out at somewhat higher temperatures, dependent on the amount of methanol present, I have found that best results are obtained when operating within the above-stated temperature range.

I have also found that the amount of methanol which may be satisfactorily employed in the method of my invention, so that the neutralization 01' the dithiophosphoric acid esters will proceed to completion without interruption is within the range of from about 0.5% to about 5.0% based on the weight of the salt-oil solution. While the amount of methanol depends, to some extent on the composition of the mixture, ordinarily from about 1% to about 2-3% will permit the neutralization reaction to proceed satisfactorily. This amount of methanol may be added to the oil and substantially all of it remains in the solution without .causing turbidity in the final dithiophosphoric acid ester-in-oil solution. Furthermore, and entirely unexpectedly, I have found that despite the presence of this small amount of methanol, the flash point of the lubricating oil compounded with the so-prepared addition agents is not lowered.

Thus, I have provided a novel method for the neutralization of esters of dithiophosphoric acids which eliminates the necessity for removal of the solvent material, and results in a neutral solution of the salt in mineral oil by the inclusion, in the neutralizing medium, of an amount of methanol not substantially greater than 5 based on the weight of the salt-oil solution. In my Patent No.i2,466,408 I have described a method wherein, in certain instances, a small amount of water is employed instead of the methanol of the present invention.

In carrying out the method of the invention the dithiophosphoric acid ester is added with vigorous agitation to a suspension in mineral oil, containing from 0.5% to 5.0% of methanol, of an oxide or hydroxide such as barium oxide, or the like. The oil suspension containing the neutralizing agent may be preheated, if desired, to from about 50 C. to about 70 C. before addition of the acid ester and the neutralization reaction, being of an exothermic nature, is controlled by cooling to a temperature not exceeding about 90 C. during the addition of the acid ester. Inasmuch as the boiling point of methanol is approximately 65 C., it might be expected that evaporation thereof would occur at those neutralization temperatures given above which are in excess of 65 0., thus leaving the solutions and/or dispersions free of the methanol solvent and causing the reaction to stop. However, it is also a well-recognized scientific fact that the boiling point of any solvent is raised by the addition thereto of a non-volatile solute. Although the .usual physical chemistry textbook equations of Raoults law permit the calculation of the elevation of boiling points when the solutions involved are quite dilute, by employing a variation of these equations it may be estimated with a reasonable degree of certainty that my neutralized dithiophosphoric acid ester salt-oil solution containing not more than 5% methanol will not boil below about 90 (3., and that solutions containing lesser amounts of methanol will have appreciably higher boiling points.

In practicing the present invention, it has been found that methanol is still present after completing the neutralization treatment even though temperatures as high as 90 C. have been employed. It is to be understood, however, that there is some small degree of evaporation of the methanol since the neutralization step is usually carried out in open vessels. However, the amount of methanol remaining in the solution has not been reduced below that amount necessary to carry out complete neutralization of the acid dithiophosphoric esters, which is usually about 0.5%, based on the weight of the salt-oil solution.

I have found that, in carrying out the neutralization treatment, optimum results are obtained when the quantity of acid ester employed is substantially equal to, but not greater than, the quantity of oil in the dispersion containing the base material and methanol. The neutraliz ing agent employed may range from about 1 to tained by the preparation of a neutral solutions of 50% dilution, of the heavy metal salts of esters of dithiophosphoric acid in mineral oil containing up to about 2% of methanol after filtration of the solution to remove excess neutralizing agent and oil-insoluble salts formed during the neutralization reaction.

Ordinarily, the mineral oil solutions of heavy metal salts of dithiophosphoric acid esters obtained by the method of my invention are clear liquids, indicative of the substantial absence of water. During the neutralization reaction one of the by-products formed is water which, if it exists in the final product in appreciable excess of about 0.3% of the total volume of solution, will cause slight turbidity of the acid salt-mineral oil solution. If it is desirable to remove such excess water, for the purpose of improving the appearance of the solution, the neutralized solutions and/or dispersions may be subjected to "flash stripping, wherein the material is momentarily heated after which the heated material is admitted to an evacuated chamber, permitting the almost instantaneous evaporation of most of the water and methanol along with a simultaneous lowering of the temperature of the liquid. Alternatively, it may be desirable to remove any excess of water by the addition of a small amount of CaSO4 such as anhydrite or calcined gypsum to the solution and/or dispersion. After filtration, the mineral oil solution of the heavy metal salt of the dithiophosphoric acid ester will be entirely clear, the small amount of methanol still present causing no turbidity of the solution. There is no actual need for removing the excess water inasmuch as it does not detract from the antioxidant and detergent qualities of the improvement agent.

The invention will be illustrated in greater detail by the following examples showing specific embodiments thereof. The examples, however, are intended for purposes of illustration only, the limits of the invention being defined by the appended claims.

Example 1 In the preparation of an ester of dithiophosphoric acid there was employed a mixture of alcohols obtained by the catalytic hydrogenation of coconut oil, containing straight-chain alcohols of from 3 carbon atoms to 18 carbon atoms content, which is described in Example 4 of U. S. Patent No. 2,005,619. In this example, lbs. of the alcohol mixture and 34 lbs. of P285 were heated for 2 /2 hours to yield lbs. of a mixed dithiophosphoric acid ester. This acid mixture was I added to an S. A. E. 10 grade lubricating oilbarium oxide-methanol slurry which contained 1.13 lbs. of oil and 0.2 lb. of BaO per pound of acid employed. The amount of methanol was approximately 2% of the product. The acid addition was started with the oil, etc., slurry at a temperature of 25 C., the temperature rising to, and being held at, 50 C. during the reaction. After filtering to remove oil-insoluble salts formed during the neutralization reaction and excess BaO, the solution contained about 0.3% of water, which was reduced to 0.2% by the addition of a small amount of @1804 followed by filtration. The product was a clear solution which had a Saybolt viscosity of 112.4 at F.

The addition agent so prepared was added in an amount of 2% by volume to a commercial 5 lubricating oil. Tests of the lubricating oil containing the additive showed that the flash point of the oil had not been lowered by the addition of the agent. This material was tested in a Chevrolet automobile engine in a continuous run of 36 hours. Test results are as follows:

Addition Agent Addition Agent Containing 2% Prepared by Methanol Prepared Prior Method by the Method of Employing Solvent the Present Removal Pro- Invention cedure Total sludge and varnish rating 99. 3 93. Bearing corrosion, weight loss in gms 0. 039 l. 558 Viscosity SUS at 100 F;

New 172 178 The total sludge and varnish rating is based on inspection of the cylinders, pistons, and piston rings for varnish deposition, and on inspection of the oil for sludge content. Total absence of both is given a rating of 100.

Example 2 A mixture of alcohols and phenols composed of 20% octyl phenol, 20% methyl isobutyl carbinol, 10% capryl alcohol, and the balance a distillation fraction of the by-product alcohols obtained in the synthesis of methanol, boiling between 160 C. and 200 C. and consisting predominantly of 7 and 8 carbon atom alcohols, and described in U. S. Patent No. 2,368,000 was treated with P285 to form the corresponding mixed diester of dithiophosphoric acid. The equivalent weight of this acid product was 450.

159 grams of S. A. E. 10 grade lubricating oil, 28 grams of barium oxide, and 16 grams of methanol was charged to a 1 liter flask fitted with a mechanical agitator, and to which a condenser was attached. The weight of the methanol was calculated so as to be about by weight of the finished product. The mixture was heated to 70 C. and 138 grams of the above described diester of dithiophosphoric acid was added over a period of about minutes. The temperature rose to 76 C. as a result of the reaction. The resulting mixture was heated and stirred for minutes at a temperature of 80 C.-90 C. The product gave an alkaline test to phenol-phthalein indicator, showing the neutralization to be complete. The resulting solution or dispersion was filtered, the filtrate being clear and bright and entirely suitable for use as a lubricating oil addition agent without further treatment. An examination of the condenser and receiver at the end of the experiment showed that less than 1 gram of methanol had been lost by evaporation.

From the foregoing description it will be readily apparent that the present invention provides a method of preparin antioxidant and detergent agents whereby the process has been rendered moreeconomically practicable than those of prior use, and the products exhibit increased effectiveness over those previously obtained by other methods, by the provision of a method of preparing dithiophosphoric acid ester salts in mineral oil solution and/or dispersion, and wherein the removal of solvent material i rendered unnecessary.

What I claim is:

1. Process for preparing a solution in mineral oil of a heavy metal salt of an oil-soluble ester of dithiophosphoric acid which comprises the steps of adding an oil-soluble ester of dithiophosphoric acid to a dispersion in mineral oil of a member of the group consisting of the oxide and hydroxide of barium, said dispersion containing from about 0.5% to about 5.0% of methanol, reacting the said materials at a temperature of from about 20 C. to about C. while retaining in the solution an amount of methanol suflicient to carry out complete neutralization of the acid dithiophosphoric ester, and removing the oil-soluble reaction salts by filtration.

2. Process for preparing a solution in mineral oil of a. heavy metal salt of an oil-soluble ester of dithiophosphoric acid which comprises the steps of adding an oil-soluble ester of dithiophosphoric acid to a dispersion in mineral oil of barium oxide, said dispersion containing from about 0.5% to about 5.0% of methanol, reacting the said materials at a temperature of from about 20 C. to about 90 C. while retaining in the solution an amount of methanol sufiicient to carry out complete neutralization of the acid dithiophosphoric ester, and removing the oil-insoluble reaction salts by filtration.

3. Process as in claim 2, and wherein the methanol is present in an amount of from 1% to 2%.

CHARLES EARLE FUNK, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. PROCESS FOR PREPARING A SOLUTION IN MINERAL OIL OF A HEAVY METAL SALT OF AN OIL-SOLUBLE ESTER OF DITHIOPHOSPHORIC ACID WHICH COMPRISES THE STEPS OF ADDING AN OIL-SOLUBLE ESTER OF DITHIOPHOSPHORIC ACID TO A DISPERSION IN MINERAL OIL OF A MEMBER OF THE GROUP CONSISTING OF THE OXIDE AND HYDROXIDE OF BARIUM, SAID DISPERSION CONTAINING FROM ABOUT 0.5% TO ABOUT 5.0% OF METHANOL, REACTING THE SAID MATERIALS AT A TEMPERATURE OF FROM ABOUT 20*C. TO ABOUT 90*C. WHILE RETAINING IN THE SOLUTION AN AMOUNT OF METHANOL SUFFICIENT TO CARRY OUT COMPLETE NEUTRALIZATION OF THE ACID DITHIOPHOSPHORIC ESTER, AND REMOVING THE OIL-SOLUBLE REACTION SALTS BY FILTRATION. 